U.S. Pat. No. 7,066,279, the contents of which are incorporated by reference herein, relates to a ground piercing tool which includes a housing and an air distributing mechanism that reciprocates a striker to impact a bit shaft in response to a supply of compressed fluid. A fluid inlet tube is mounted in the bore of the striker. A rear end of the inlet tube is in communication with the distributing mechanism, wherein the housing and bit shaft cooperate to define a front chamber that decreases in volume as the chisel moves forward relative to the housing, and wherein the bit shaft has a radial passage therein that conducts compressed fluid from the inlet tube to the front chamber, which is configured to form an air spring. The present invention is an improvement to the air spring concept as expressed in U.S. Pat. No. 7,066,279 and operates in the same manner except as described hereafter.